Field of the Invention
The invention relates to the technical field of the herbicides and plant growth regulators, namely substituted 4-cyano-3-(pyridyl)-4-phenylbutanoates, which can be used for controlling unwanted vegetation, for the selective control of broad-leaved weeds and weed grasses in crops of useful plants and also for regulating and influencing plant growth of crop plants. Moreover the invention relates to processes for preparing substituted 4-cyano-3-(pyridyl)-4-phenylbutanoates and/or salts thereof.
Description of Related Art
Since, from the prior art listed and analysed below, 4-cyano-3-(heteroaryl)-4-phenylbutanoates—including individual herbicidal 4-cyano-3-(pyridyl)-4-phenylbutanoates—are already known, the invention relates in particular to substituted 4-cyano-3-(pyridyl)-4-phenylbutanoates, to processes for their preparation and to their use as herbicides and plant growth regulators.
Document EP 0 005 341 A2 discloses esters and amides of 4-cyano-3,4-diarylbutanoic acids and their herbicidal action. Also disclosed in generic form, in addition to 4-cyano-4-phenyl-3-phenylbutanoates and 4-cyano-4-heteroaryl-3-phenylbutanoates, are 4-cyano-3-heteroaryl-4-phenylbutanoates, where the definition of heteroaryl comprises, in addition to thienyl, also pyridyl. However, in the specific examples disclosed in EP 0 005 341 A2, the 4-cyano-3,4-diphenylbutanoic acids and their esters predominate, whereas the pyridine-substituted compounds are limited to two specific examples, namely 4-cyano-3-phenyl-4-(pyridin-3-yl)butanoic acid and its ethyl ester. In contrast, EP 0 005 341 A2 does not disclose any specific examples of 4-cyano-3-pyridyl-4-phenylbutanoates.
According to the teaching disclosed in EP-A-0 005 341 A2, the threo isomers of the compounds disclosed in EP 0 005 341 A2 are generally suitable for the non-selective control of harmful plants, whereas the erythro/threo isomer mixtures are preferred for the selective control of harmful plants in some crops of useful plants. Using 4-cyano-3,4-diphenylbutanoic acid unsubstituted in the phenyl radical as an example, EP 0 005 341 A2 furthermore shows that the two isomers which belong to the threo form have different activities.
Document EP 0 270 830 A1 discloses that threo isomers and erythro/threo isomer mixtures of 4-cyano-3,4-diarylbutanoic acid (esters) can be used as plant growth regulators, preventing the development of an infructescence in various harmful grasses. The aryl groups envisaged are unsubstituted or substituted phenyl radicals and also unsubstituted pyridine radicals or halogen-substituted pyridine radicals. The examples disclosed in document EP 0 270 830 A1, which mainly relate to (substituted) 4-cyano-3,4-diphenylbutanoic acid (esters), also include two specific 4-cyano-3-pyridyl-4-phenylbutanoic esters (cf. the first two compounds in Table Ig on page 33), namely ethyl 4-cyano-3-(pyridin-3-yl)-4-phenylbutanoate and methyl 4-cyano-3-(pyridin-4-yl)-4-(3-chlorophenyl)butanoate.
Document JP 04297454 A discloses 4-cyano-3-heteroaryl-4-phenylbutanoates and their use as herbicides. The heterocycles representing the letter “A” and the heterocycles located in the 3-position of the butanoate include, in addition to an unsubstituted quinoline, also a methyl-substituted pyridin-2-yl radical (6-methylpyridin-2-yl).
Document WO 2010/114978 A1 relates to the preparation of pharmaceutically active compounds (renin inhibitors). For the preparation of the renin inhibitors, the document discloses the use of 4-cyano-3-(3-pyridyl)-4-phenylbutanoates whose pyridine radical is substituted by a methoxy group.
The scientific publication published in Biorganic & Medicinal Chemistry Letters 22 (2012) 1953-1957 also relates to the preparation of pharmaceutically active compounds (renin inhibitors) and, in this context, discloses the use of ethyl 4-cyano-3-(heteroaryl)-4-phenylbutanoates (cf. compound 3 in Scheme 1 page 1955 in combination with Table 1, in which the aryl radicals referred to as Y are specified, on page 1954). According to Table 1, Y in the compound 37 mentioned refers to a pyridin-3-yl. Thus, during the synthesis of compound 37, in a first reaction step, by Michael addition (cf. Scheme 1), one of the intermediates formed was the compound ethyl 4-cyano-3-(pyridin-3-yl)-4-(2-chloro-4-bromophenyl)butanoate.
In their application, the crop protection agents known to date for the selective control of harmful plants in crops of useful plants or active compounds for controlling unwanted vegetation sometimes have disadvantages, be it (a) that they have no or else insufficient herbicidal activity against particular harmful plants, (b) that the spectrum of harmful plants which can be controlled with an active compound is not wide enough, (c) that their selectivity in crops of useful plants is too low and/or (d) that they have a toxicologically unfavourable profile. Furthermore, some active compounds which can be used as plant growth regulators for a number of useful plants cause unwanted reduced harvest yields in other useful plants or are not compatible with the crop plant, or only within a narrow application rate range. Some of the known active compounds cannot be produced economically on an industrial scale owing to precursors and reagents which are difficult to obtain, or they have only insufficient chemical stabilities. In the case of other active compounds, the activity is too highly dependent on environmental conditions, such as weather and soil conditions.
For the reasons mentioned, there is still a need for alternative, highly active herbicides for the selective application in plant crops or use on non-crop land. It is also desirable to provide alternative chemical active compounds which may be used in an advantageous manner as herbicides or plant growth regulators. Likewise desirable are compounds having herbicidal activity which are highly effective against economically important harmful plants even at relatively low application rates and can be used selectively in crop plants, preferably with good activity against harmful plants.
Against this background and against the background of the prior art analysed above, it was an object of the invention to provide alternative 4-cyano-3-(pyridyl)-4-phenylbutanoates not having the disadvantages of the compounds known from the prior art and suitable for use in crop plants or else on non-crop land and as plant growth regulators.
Particularly desirable are compounds having herbicidal activity which are highly effective against economically important harmful plants even at relatively low application rates and can be used selectively in crop plants, preferably with good activity against harmful plants.